Air purification systems are known in the art. WO2004/112958, for instance, describes a gold/titanium dioxide photo catalytic/thermocatalytic coating which simultaneously oxidizes volatile organic compounds and carbon monoxide that adsorb onto the coating, into water, carbon dioxide, and other substances. The gold has a size less than 3 nanometers. When photons of the ultraviolet light are absorbed by the gold/titanium dioxide coating, reactive hydroxyl radicals are formed. When a contaminant is adsorbed onto the gold/titanium dioxide coating, the hydroxyl radical oxidizes the contaminant to produce water, carbon dioxide, and other substances. Gold is an oxidation catalyst that lowers the barrier energy of carbon monoxide to oxide the carbon monoxide to carbon dioxide. Therefore, the gold/titanium dioxide coating can also simultaneously oxidize carbon monoxide to carbon dioxide.